Excluding those mentioned above, sealed beam lighting systems used in motor vehicles, and in particular those for providing forward illumination for automobiles, have generally not been designed with aerodynamic considerations in mind. As such, these lighting systems have exhibited poor aerodynamic performance. The typical minimum height of headlamps found in such lighting systems is no less than about four inches (some as high as seven inches), including systems having four rectangular headlamps (two per side) as part thereof. Of equal importance is the total area of the headlighting system when viewed from the front. In many existing systems, total vertical areas of about seventy to ninety square inches are common. Understandably, such large areas contribute to poor aerodynamic performance of the respective motor vehicles. In this regard, the following table is a list of many existing (again excluding those mentioned above) multiple headlamp lighting systems illustrating the approximate height and total frontal (vertical) area of each system listed.
TABLE ______________________________________ Approximate Approx. Total System Headlamp Height Area System Type (Inches) (Sq. Inches) ______________________________________ Sealed Beam Headlamps 2 Lamp, Round 2D 7 77 4 Lamp, Round IC/2C 51/4 87 2 Lamp, Rectangular 2B 51/2 83 4 Lamp, Rectangular 1A/2A 4 96 2 Lamp, Rectangular 2E 4 48 ______________________________________
In a system not referred to in the above Table, a lamp capsule element is replaced in a fixed reflector-lens combination (i.e., through a rear opening in the reflector). However, with this system, there exists the potential for a tolerance control problem, in particular between the positional arrangement of the lamp's filament and the reflector. With lighting systems such as the aforementioned replaceable system and those mentioned in the Table above, there is also the problem that when a headlamp burns out, a major portion of the forward light pattern is lost due to the inability of only the single headlamp remaining (in a two headlamp arrangement) to provide sufficient forward illumination. In a four headlamp system (two per side) a significant reduction in output on one side of the vehicle occurs. Still another problem in the above systems with separate headlamps being used for high and low beam is the inherent lack of flexibility, particularly in optimizing both high and low beam patterns. In those systems in which two filaments are employed in a single lens-reflector combination, the lens element can typically be optimized for only one pattern. Switching to the second filament results in a compromised light distribution.
Lastly, and perhaps most significantly, headlamp systems of the replaceable type and of the type described in the above Table typically mandate relatively complex alignment procedures (which are usually only capable of being accomplished by a skilled technician) to both maintain the headlamp in required alignment and to assure that a replacement therefor is in turn also correctly oriented within the vehicle. Examples of such procedures, and the various complex vehicle structures necessary to achieve these, are shown in U.S. Pat. Nos. 4,188,655, 4,471,413 and 4,503,486. Understandably, the requirement for such apparatus adds to the cost of the headlamp system as well as that of the vehicle utilizing same.